1. Field of the Invention
The present invention generally relates to auxiliary power units and, more particularly, to auxiliary power units for use on transport vehicles powered by internal combustion engines to provide electrical power during periods when the transport vehicle's main engine must be shut off.
2. Description of the Prior Art
Approximately one-half million diesel-powered trucks provide long-haul transport of goods throughout the United States. A common practice among truckers is to leave the diesel engines that power these trucks running—i.e., idling—during overnight stops. This practice occurs for a number of reasons, such as (1) to keep the cab and/or the sleeper compartment warm or cool; (2) to keep the diesel fuel warm during the winter months; (3) to keep the engine warm to avoid cold starting problems; (4) to mask other noises; (5) to enable use of various electrical devices in the truck cab, and the like. Idling these large engines burns significant amounts of fuel, far in excess of the amount needed to provide power for these benefits to the drivers. Such diesel fuel consumption needlessly consumes a non-renewable energy resource, burdens the costs of shipping goods with unnecessary expense, and results in significant amounts of air and noise pollution. Idling the engines of these transport vehicles for substantial periods of time also violate various federal, state and local laws and regulations. In addition to the costs of the wasted fuel and the environmental impacts of overnight idling are the higher maintenance costs due the excess wear that results from running the engines for uses other than pulling a loaded trailer and increased health costs to treat illnesses caused by the emissions from the engines.
A number of solutions to the idling problem have been developed and are currently in use. These conventional systems generally employ an auxiliary power unit (APU) that runs on diesel fuel and drives an electric alternator or generator to supply operating voltages for heating and cooling the cab and/or sleeper compartment (“cabin”) or recharging the truck battery. However, each of these conventional systems has one or more of the following disadvantages: (1) the engine of the APU is water cooled and must be tied into the radiator system of the truck or be provided with its own radiator, hoses, water pump, etc.; (2) the engine of the APU drives the alternator or generator via a belt drive, which is associated with reduced efficiency, reliability, and additional maintenance costs; (3) the APU mechanically drives the A/C compressor for an auxiliary cooling system located in the cabin of the truck; (4) the alternator or generator in the APU requires an inverter or converter to provide a second output voltage in addition to the one it produces; (5) the APU requires extensive integration into the truck fuel, cooling, exhaust and electrical systems, which increases the cost of installing and maintaining the APU and reduces the reliability of the combined systems; (6) the integration of the APU into the truck systems increases the mechanical complexity thereof resulting in reduced reliability; and (7) the APU itself tends to be heavier and less efficient than it could be using modern technology.
As an illustration, conventional auxiliary power units are typically liquid cooled and require a radiator, a water pump, hoses, thermostat, etc., along with the mechanical structure to support them. Conventional auxiliary power units also use some form of adapter that employs a belt, chain, clutch or gear set to couple the engine to the generator, which adds weight, mechanical complexity and additional maintenance requirements. Further, conventional auxiliary power units typically require a converter circuit to produce a DC voltage from the generated AC voltage output or an inverter circuit to produce an AC voltage from the generated DC voltage output. In either case, the additional circuitry adds weight, complexity, maintenance requirements and cost, all without improving the conversion efficiency of the auxiliary power unit. Efficiency is reduced in any of these conventional auxiliary power units because the motive power supplied by the engine must be large enough to overcome the extra losses associated with the more complex conventional auxiliary power units.
What is needed is an efficient, compact APU of minimal complexity that overcomes the above disadvantages, is easily integrated into an existing installation with an auxiliary heating and cooling unit, and directly and efficiently provides both AC and DC electrical power for the cabin and for battery recharging at minimum cost.